1. Field of the Invention
This invention relates to a method and apparatus for filtering hot cooking oil such as that used in commercial deep fryers. In particular the invention relates to a method and apparatus for straining the oil by passing it under a relatively low positive pressure through a filter pad of substantially uniform thickness and pore opening held in a pressure chamber. The filter pad includes fibrous material and activated carbon held by a resin binder.
2. Description of the Prior Art
It has long been known that cooking oils, such as those used in commercial or institutional deep fryers, tend to become contaminated with such things as moisture and carbonized food particles during frying. The oils also tend to break down chemically after extended use, often causing the oil to foam, smoke, smell bad, look bad or taste bad. It has been found that keeping the cooking oil clean by removing the particulate matter and filtering it on a regular basis tends to extend the useful life of the cooking oil and increase the quality and appearance of foods which are cooked therein. In commercial and institutional cooking operations it has been found necessary to filter cooking oil as often as every eight hours. To reduce the down time of the cooking machine it is desirable to filter the oil while it is hot, usually in the 350.degree. to 370.degree. F. range, and to complete the filtering procedure as quickly as possible. While specialized filtering apparatus of many types have been proposed in the past, the filtration process has remained time consuming, disruptive of business and less than satisfactory in extending the life of the cooking oil.
In particular, equipment employing a vacuum to draw cooking oil downwardly through a filter which has been sprinkled with diatomaceous earth or the like has been employed in equipment sold by the Dean-Alco Company. Similar equipment is also disclosed in U.S. Pat. No. 4,043,916. Equipment employing a two step filtration process involving drawing the cooking oil through a relatively coarse filter by means of a vacuum and then pumping the cooking oil upwardly through a thick, tightly wound paper filter is disclosed in U.S. Pat. No. 4,517,082. Similar equipment employing a crepe paper filter is disclosed in U.S. Pat. No. 4,591,434.
It is also known to include a filtering system within a deep fat fryer for filtering oil on a continuing basis and U.S. Pat. No. 4,668,390 discloses such a device wherein the filter element comprises a carbon-impregnated cloth.
Attempts have been made to force cooking oil under high pressure downwardly through a filter loosely covered with diatomaceous earth or other particulate filtering material. Such equipment has proven unsuccessful because of the non-uniformity of the thickness and pore opening of the particulate material spread on the filter and the tendency of the oil to mainly pass through parts of the filter which are the least thickly covered with the particulate filter material. In addition, filtration at relatively high pressures, i.e., above 40 PSI, has been found to speed the chemical breakdown of cooking oil, thus shortening its useful life.